Surface inclusions and their evolution on strip rolled on CSP line and in following cold rolling process

Abstract

Hot and cold rolled strip samples with surface defects such as black pockmark, sliver and central cracking were collected from a compact strip production line followed by cold rolling. Microstructures and chemical compositions of the strip with defects were studied by scanning electronic microscopy and energy dispersive X-ray spectroscopy. Four typical types of defects on strip including surface spherical mould powder entrapment, centre spherical mould powder entrapment, surface linear mould powder entrapment and centre linear mould powder entrapment were studied by hot and cold rolling experiment in laboratory. It was observed that spherical mould powder entrapment was transformed into the surface black pockmark after the hot rolling and cold rolling process. Centre spherical mould powder entrapment led to central fracture in the hot and cold rolling process. Surface linear mould powder entrapment resulted in sliver and centre linear mould powder entrapment led to severe sliver.     

DEFORMATION AND DENSIFICATION DURING THE ROLLING OF METAL POWDERS

Abstract

The deformation of particles and the general process of densification during the roll-compacting of strip from metal powder have been determined by photomicrographic and QTM studies. Observations were made on the expansion of the compacted strip after it had passed the plane joining the roll axes. The effect was related to elastic recovery of the material and the expansion of gases entrapped in the pores between the particles.

The production of satisfactory green strip was found to be restricted to a range of thicknesses obtained between certain maximum and minimum roll gaps. These limits were related to roll pressure and strip density. It was also restricted by a maximum rolling speed that was governed by powder flow to the compaction zone.

Density variations that occurred across the width and through the thickness of green strip were also determined.     

THE COMPACTION OF METAL POWDERS BY ROLLING. I.—THE PROPERTIES OF STRIP ROLLED FROM COPPER POWDERS

Abstract

The investigation described is an extension of earlier work (“Symposium on Powder Metallurgy 1954”, p. 131. 1956: London (Iron and Steel Institute), and Sheet Metal Ind., 1955, 32, 589) which described the effect of rolling pressure and sintering conditions on the mechanical properties of strip rolled from copper powders. The directional variation of U.T.S. and of elongation of sintered strip are shown to be the same as those of solid copper with a similar microstructure, at least for material with up to 16% porosity. The shape of powder particles and the particle-size distribution have a marked effect on the strength of sintered strip by virtue of their effect on the shape and size of the pores in the sintered material. Measurements of electrical resistance reveal a linear relationship between conductivity and porosity over wide ranges of porosity in both “green” and sintered strip. The conductivity increases rapidly during the first few minutes of sintering at 1000° C. Measurements of the resistance in the rolling direction and in the transverse direction, which are independent of local variations in density, have been made on green sheet; the resistance in the rolling direction is the higher. A correlation between this result and the mode of particle deformation is proposed, and is elaborated in Part II of this paper.     

CONTINUOUS COMPACTION BY CYCLIC PRESSING

Abstract

A process recently developed produces wide, thick bars of unlimited length from powder, granular, or sponge raw materials by a cyclic pressing operation. The process can be adapted readily for laboratory study or for large-scale production.

Many materials have been pressed by this technique, and in all cases compaction was similar to that experienced in conventional pressing. Work on the pressing, sintering, and subsequent working of various nickel powders and of a nickel-iron-molybdenum magnetic alloy has been carried out. Carbonyl nickel powder produces nickel strip of high quality. A high-permeability alloy containing nickel 79, iron 17, and molybdenum 4% can be made into strip with good magnetic properties by compacting the powders with the cyclic-pressing technique and then sintering and rolling the pressed bar into strip.     

THE CONTINUOUS SINTERING OF COPPER-LEAD TO STEEL

Abstract

Bimetal strip consisting of copper-lead bonded to steel is produced by sintering uncompacted powder on to the steel, compacting by rolling, and resintering. The mechanism of the process is considered in the light of published work on liquid-phase sintering and of some experiments in which material at various stages of processing has been examined physically and metallographically. It is concluded that the process differs from normal liquid-phase sintering in that interparticle welding is brought about by the intermediate rolling process.     

PRODUCTION OF PURE NICKEL STRIP BY THE DIRECT-ROLLING PROCESS

Abstract

Results are presented of an investigation into the production of pure nickel strip, 6 in. wide × 0·030 in. thick, from carbonyl-nickel powder, using compacting rolls 7 ? in. in dia., arranged in a horizontal plane. Special reference is made to the factors affecting the quality and output of green strip: roll-gap dimensions, the head of powder above the roll gap, rolling speed, and raw-material properties. It is shown that for a given compacting mill, the thickness of green strip that can be produced is strictly limited and that it becomes progressively more difficult to achieve the limiting thickness with increase in rolling speed. A method of reducing the detrimental effect of high rolling speeds is described.

The continuous sintering and subsequent processing of directly rolled strip, using conventional cold-rolling and annealing plant, are then considered, and the properties of fully processed material are compared with those of strip produced from melted and cast carbonyl-nickel pellet. It is concluded that the direct-rolling process is capable of producing on a commercial basis nickel strip having properties which compare favourably with those of conventionally produced material.     

THE PRODUCTION OF CERMETS CONTAINING A RELATIVELY LARGE AMOUNT OF DISPERSED PHASE

Abstract

The preparation and related properties of dispersions of ceramics in metallic matrices are reviewed, with particular reference to recent British work in this field. There have been substantial advances in the fabrication of cermets by powder metallurgy, particularly those based on UO₂ or PUO₂ and stainless steel, it being now possible to manufacture almost perfect dispersions in bar or strip form. Some closer understanding of the mechanical properties of cermets or porous matrices has been achieved. These theoretical and technological developments are capable of wide application to non-nuclear materials.     

Effects of adding overspray powder on microstructures and mechanical properties of spray deposited 8009 aluminium alloy

Abstract

Under normal condition the cooling rate in a spray deposition process is too low to form 8009 aluminium alloy. In order to increase the cooling rate, overspray 8009 aluminium alloy powders were added. The effects of adding overspray powder on microstructures and mechanical properties of the spray deposited 8009, with and without addition of the overspray powders, were studied. It is shown that adding proper content of overspray powders significantly improves the mechanical properties of the spray deposited 8009 alloy. The mechanism involved in modification of the microstructures and the mechanical properties of the spray deposited 8009 alloy produced with the overspray powder addition approach was discussed.     

Sintering and tribological properties of lead-free bronze alloy for friction materials

Abstract

A lead-free bronze alloy powder with a dispersed sulphide solid lubricant phase has been produced by atomisation as a substitute for lead bronze friction materials. The powder has been processed to produce a bronze/steel bimetal strip by a sinter/roll/sinter process route, via both solid state and liquid phase sintering. Friction properties of the developed materials and a sintered bronze were compared in pin-on-disc tests; the Cu–Sn–S material shows excellent properties, equivalent to those of a lead bronze, and is being assessed for use in high pressure bushes.     

Comparison of thermal and microwaveassisted plasma sintering of nickel–diamond composites

Abstract

R&;D efforts at CSIRO, Australia, into the production of ‘lower cost’ titanium powders are complemented by a strong, downstream PM programme. One of these efforts has focused on the direct powder rolling of commercially pure (cp) titanium powder with a view to the continuous production of fully dense strip. Considerable research is also being undertaken to produce titanium alloy strip, initially from the Ti–6Al–4V alloy, using this process. An experimental design approach has been employed to establish key parameters, maximise the process window and meet property specifications. Demonstration of a proof-of-system at pilot scale is well advanced and the focus is now shifting to seeking industrial engagement with a view to collaboration, technology transfer and commercialisation of the technology. The current status of the technology is surveyed including aspects of the associated market trends and commercial feasibility.     

Online mechanical property prediction system for hot rolled IF steel

Abstract

Traditionally, mechanical property estimation is carried out by destructive testing, which is costly and time consuming. Sometimes, the time schedule in the mill is so tight that coils are dispatched, while the samples are still under investigation; thus, knowledge of the strip quality immediately after rolling without mechanical testing can save a lot of time and money. As the rolling process is complex and final mechanical properties of steel depend on many parameters, it is almost impossible to develop an accurate first principle based mathematical model, so an artificial neural network based model to predict the mechanical properties of hot rolled steel strip has been developed. This paper describes the neural network based online system that helps in predicting mechanical properties of interstitial free (IF) steel strip and also elaborates how this models can help in capturing various metallurgical phenomena during rolling.     

Synthesis of ultrafine WC/Co powder by mechanochemical process

Abstract

A new approach to produce ultrafine WC/Co powder by a mechanochemical process was made to improve the mechanical properties of advanced hardmetals and to cut production costs. For powder preparation, the water soluble salts containing W and Co components were used as starting materials. After synthesis of the precursor powder from an aqueous solution by a spray drying technique, a salt removing heat treatment in air atmosphere was carried out to prepare the oxide powder. The oxide powder was mixed with carbon black by ball milling and this mixture was converted at 800^oC to the nanophase WC/Co powder in H₂ and N₂ atmospheres. The average size of the WC particle was 100-150 nm. The possibility of achieving high density sintered material with an ultrafine and homogeneous microstructure using grain growth inhibitors, such as tantalum and vanadium carbides, has been shown.     

Microstructural and mechanical properties of injection moulded gas and water atomised 17-4 PH stainless steel powder

Abstract

This paper describes the microstructural and mechanical properties of injection moulded 17-4 PH stainless steel gas and water atomised powder. Gas and water atomised stainless steel powders were injection moulded with wax based binder. The critical powder loading for injection moulding were 62·5 and 55 vol.-% for gas and water atomised powders respectively. Binder debinding was performed using solvent and thermal method. After dedinding the samples were sintered at different temperatures for 1 h in pure H₂. Metallographic studies were conducted to determine to extend densification and the corresponding microstructural changes. The results show that gas atomised powder could be sintered to a maximum (98·7%) of theoretical density, and water atomised powder could be sintered to a maximum (97·08%) of theoretical density. Maximum tensile strength was obtained for gas atomised powder sintered at 1350°C. The tensile strength of the water atomised powder sintered at the same temperature was lower owing to higher porosity. Finally, mechanical tests show that the water atomised powder has lower mechanical properties than gas atomised powder.     

Consolidation and green body characteristics of gelcast metallic powder

Abstract

A preliminary study concerning the compaction of metallic powder was carried out in order to investigate a rarely explored route in powder metallurgy, to form complex geometry parts, known as gelcasting. Green bodies produced with as supplied stainless steel powder showed a tendency to form foam, which affected the surface finishing. The mechanical behaviour of green compacts was also affected by the processing additives present in the metallic powder. Organics in the as supplied powder were removed by thermal treatment at 500°C and additional samples were produced. Although no difference in green density was observed, these samples displayed better surface finish and mechanical characteristics, as a result of improved adhesion between the polymer network and particle surface. The results showed that the gelcasting process is able to produce green parts suitable for subsequent thermal treatment.     

Some Mechanical Properties of Powder-Forged Iron/Alloy Mixtures

Abstract

An investigation was made of the feasibility of producing alloy forgings (nominal composition Fe–0·5C–0·6% Mn), from a powder prepared by mixing the alloying additions with iron powder. The carbon was added as microcrystalline graphite and the manganese as elemental powder and as ferro-manganese powder. Additions of copper and ammonium chloride powders were also made for the purpose of assisting the manganese to alloy with the iron. The copper addition improved the tensile strength but lowered the ductility. The ammonium chloride had little effect except for an apparent lowering of hardness. It was found that useful mechanical properties could be obtained in forgings made from mixtures of the alloying ingredients.     

INFLUENCE OF IRON POWDER TYPE ON THE PROPERTIES OF SINTERED IRON AT VARIOUS DENSITY LEVELS

Abstract

The properties of various commercial and experimental iron powder types and of compacts made from them in the density range 6·8–7·87 kg/dm³ by single-pressing, double-pressing, and hot-forging techniques have been determined. It was shown that the ductility in all cases was more adversely affected than the tensile strength by the presence of porosity. However, it was also shown that at any particular density level or with a given processing schedule the mechanical properties varied widely, depending on the iron powder used. On the basis of the mechanical-property results, the powder types to be preferred at different density levels are indicated.     

Sintering of maraging steel with phosphorous additions

Abstract

The aim of this study was to develop a steel powder system for rapid tooling applications. The properties required are rapid densification, dimensional precision, high mechanical strength and corrosion resistance. To this end, the densification and microstructural development of a loose packed 200 grade maraging steel powder sintered with ferrophosphorous additions was examined. Liquid initially formed from a reaction of the Fe₃P and carbon, which was a residue of the polymeric binder used to shape the powder compact. This liquid caused a burst of sintering which ceased as the liquid dissipated. On further heating, a phosphorous rich supersolidus liquid appeared at triple points and grain boundaries leading to rapid densification and a sintered density of 98%.     

Synthesis and properties of Cu–Al–Ni shape memory alloy strips prepared via hot densification rolling of powder preforms

Abstract

Cu–Al–Ni shape memory alloy strips were successfully prepared by a powder metallurgy route consisting of preparing powder preforms from premixed Cu, Al and Ni powders by cold compaction, stepwise sintering in the range 873–1273 K, followed by unsheathed multipass hot rolling at 1273 K in protective atmosphere. The densification behaviour of the sintered powder preforms during hot rolling has been discussed. Homogenisation of the hot rolled strips was carried out at 1173 K for 4 h. It has been shown that the finished Cu–Al–Ni alloy strip consisted of self-accommodated plates ofβ' and γ' martensites together with a small amount of nanocrystalline Cu₉Al₄ phase. The finished hot rolled Cu–Al–Ni strips had fracture strength of 476 MPa, coupled with 2·5% elongation. The shape memory tests showed almost 100% recovery after 10 thermomechanical cycles in the hot rolled strips at 1 and 2% applied prestrain.     

Manufacture of metallurgical semifinished products from carbonyl nickel powder. Part 1

Summary It has been established in principle that carbonyl nickel powder can be processed into rod and strip by the technique of plastic working of sintered billets, and an appropriate technological process has been developed. The powder is pressed isostatically under a pressure of 9 kg/mm² into cylindrical billets, which are then sintered in hydrogen with a dew point between –20 and –30°C at a temperature of 1350°C for 5 h. To obtain sheet, the cylindrical billets are forged over the temperature range 1200-900°C into bars, which are first subjected to surface milling or planing and then to hot and cold rolling into sheet and strip. The resulting strip has high mechanical properties. The yield of sound metal in the processing of the powder to strip is 85%.Further work is in progress on the use of pressed sheet bars, which may be expected to shorten and simplify the fabrication process and raise the yield of sound material to 95%.Translated from Poroshkovaya Metallurgiya, No. 4 (64), pp. 29–36, April, 1968.